Journal of Fusion Energy, VoL 10, No. 3, 1991

Panel Discussion

Status and Plans for Inertial Confinement Fusion Remarks of Marshall Sluyter 1

and the inertial fusion programs from the point of view of their energy applications. Their reports, I assume, have been completed by now and should be out soon. The sum total of their recommendations have raised the level of visibility of both the magnetic and inertial fusion programs. I think it is very appropriate that we have this distinguished group of the world's scientific leaders to reflect on their various programs, and the extent to which their programs will contribute to the next step of progress in inertial fusion.

I have the privilege today of chairing this session and also of introducing to you the members of this panel. It is indeed a distinguished panel that comprises the leadership of virtually the entire inertial fusion program around the world. Two very high-level panels have completed their reviews of the DOE fusion programs. The National Academy of Sciences, in particular, has reviewed only the inertial fusion program; whereas the Fusion Policy Advisory Committee has reviewed both the magnetic i U.S. Department of Energy.

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Journal of Fusion Energy, VoL 10, No. 3, 1991

Remarks of Roger O. Bangerter 1

In a sense, each target is a different confinement scheme. In the target development area, one could try a large number of different target designs to develop the optimum target for commercial power production. The target energy yield and repetition rate can be varied over a very large range. In particular, the target yield can be arbitrarily small. Since the target yield can be small, one could build and test a variety of small, inexpensive tritium self-sufficient reactors. The ability to test these small reactors at any power level between a watt and a gigawatt is an important asset that could lead to a relatively inexpensive path for fusion energy. As mentioned, such a vision cannot be realized for 10 or 15 years. During the next 10 to 15 years, a vigorous accelerator physics and technology deveIopment program is needed. The first element in such a program should be the proposed series of induction linac system experiments (ILSE). The ILSE sequence of experiments will take about 4 to 5 years. These experiments are small, scaled experiments designed to test many of the physics issues of a full-scale accelerator. Completion of the ILSE experiments will not provide an adequate basis to build a full-scale reactor driver such as the driver illustrated in Fig. 1. We will need one more intermediate facility, perhaps at the 100-kilojoule level. The ILSE experiments and the construction of an intermediate facility at the 100-kilojoule level could lead, sometime after the turn of the century, to the construction of the large accelerator facility shown in Fig. 1. The virtues and vices of heavy ion fusion differ substantially from those of solar energy and magnetic fusion. In fact, they differ substantially from those of laser fusion. Therefore, a strong, aggressive, heavy ion fusion program would be a real asset to the country and to the world. It would significantly increase the breadth of our energy options. Incidentally, preliminary conceptual designs suggest that the cost of a large heavy ion driver would be substantially less than the cost of ITER. In summary, construction of a heavy ion driver would be a very cost-effective way to pursue fusion research.

Figure 1 shows an attractive vision for the development of commercial fusion energy. This vision is based on a large heavy ion accelerator that serves as a driver for a variety of inertial fusion research applications. Such an accelerator couldn't be designed and built in less than 10 or 15 years. It would, however, be a very valuable fusion research tool that would, to a large extent, change the way that we think about fusion development and fusion research. A large accelerator with enough power and energy to ignite a target, would be an extremely versatile research tool. One could switch the beam to a variety of experiments on a pulse-to-pulse basis similar to the way in which it is done in large, high-energy physics facilities. Thus, one could have many experiments in progress at the same time. One could have a target development area, a number of reactor development areas such as Test Reactor A, Test Reactor B, and any other miscellaneous applications that might be needed. Such a time-sharing scenario is possible because an accelerator has more than ample pulse repetition rate for fusion applications.

Versatility Accelerator

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In a sense, each target design is a different confinement scheme Target yield and repetition rate can be varied over a wide range. A variety of small, inexpensive, tritium-self-sufficient reactors could be tested. The development path to fusion energy should be relatively inexpensive. A vigorous physics and technology development plan is required to design and build such an accelerator The virtues (and vices) of HIF differ substantially from those of MFE, fission, and coal. HIF increases the breadth of our energy options significantly

Fig. 1. A large heavy ion accelerator would be a valuable fusion research tool. ' Lawrence Berkeley Laboratory.

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Journal of Fusion Energy, VoL 10, No. 3, 1991

Remarks of J. Pace VanDevender I

Not only is it going to be an exciting next few years, it also has been a very exciting last 10 months. I remember well the day in December when I was called by the Committee of the National Academy of Sciences on Inertial Confinement Fusion and they challenged us to accept a series of milestones. Those milestones were negotiated to take the light ion approach to fusion from proton experiments into the era of lithium beams. The milestones specified voltage, current, ion production efficiency, Li + purity, and divergence. My colleagues in light ions have had an exciting 10 months, meeting four out of the five milestones. The milestone on ion beam divergence was not met. We inferred that the divergence was consistent with an instability. The sine qua non of light ion fusion is the control of the instabilities associated with the electrons and ions flowing in the ion diode, the device that converts electromagnetic energy into particle beam energy. The challenge for us in the next 2 years, as specified in the committee report is to tame this beam, reduce its divergence, create a higher power density beam, and proceed with target experiments leading to a decision in FY 1992 to upgrade the PBFA II for ignition. I think that challenge is doable. We have developed the required tools. We have a 3-D PIC computer code called QUICKSILVER that predicts the beam divergence quite well for both protons and lithium. We have the diagnostics. We have a list of potential solutions that need to be screened, tested computationally and experimentally, and implemented to control the beam. If our goals are achieved, we should have a megajoule beam on PBFA II and the potential for ignition on PBFA II. I realize that the committee found that the only possible driver for ignition by the end of the decade is a glass laser. That conclusion is predicated on the assumption that the divergence of the ion beam cannot be reduced. We and our colleagues at Cornell University

and the Naval Research Laboratories are striving to reduce the beam divergence, increase the power density, drive targets, win that FY 1992 decision, and strive for ignition on PBFA II. I strongly endorse the national goal of ignition that the NAS Committee and the DOE Fusion Policy Advisory Committee recommended. I like the clear definition of issues for all programs that are outlined in the reports. I was very pleased at the recognition of the importance of low-cost and high-efficiency drivers for economical energy. Of course, these are strengths that we perceive for light ions. The National Academy of Sciences Report and the Fusion Policy Advisory Committee Report are complementary for light ions. The former told us to improve beam divergence, increase power density, and perform quality target experiments. That must be our first priority for the defense program, which does not have funding for beam propagation and standoff. Fortunately, the recommendations from the latter committee endorse the propagation and standoff technologies. Together they make an excellent package. I am very appreciative of the work that members of both committees have done. I am very thankful for the work that my colleagues at Sandia and Cornell University, the University of Wisconsin, and the Naval Research Laboratory have done, but I am very mindful of the challenge of the next 2 years. I believe the leadership of the light ion program in the United States must be a full-time job in that crucial 2-year period. Therefore, I have appointed Don Cook to be the new ICF Program Manager at Sandia to replace me effective immediately. I ask this community to support him as well as you have supported me in the past. I hope that when we come back to the annual meeting in 2 years and review the progress on those issues, Don will be able to announce that there is a second inertial fusion driver ready for an ignition upgrade.

1 Sandia National Laboratories.

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Journal of Fusion Energy, VoL 10, No. 3, 1991

Remarks of S. Nakai I

101"

Figure 1 shows the recent progress of laser fusion by pellet implosion. On the left is the increase of the neutron yield which corresponds to the temperature. On the right is the increase of the compressed densities. We have reached almost 1000 times liquid density, which is the necessary condition for the ignition with relatively small driver energy. The progress is rapid and steady during these 5 or 6 years, we can have the confidence to reach ignition. If we put the plasma parameters on an n$-T diagram, it is seen that the ignition condition is in a range which can be reached in the near future (Fig. 2). Ion temperature of 10 keV, and the maximum n'r more than 1015 see cm -3 have been reached. Figure 3 shows a strategic program toward an ICF reactor. We are now in the period for ignition and breakeven. The necessary driver energy is 100 kJ to 1 MJ. Our program has a name, "KONGHO." We are now in negotiation with the Government to start this project. The 100-kJ laser has already been designed based on the present GEKKO-XII lasers as an upgrade system. For demonstration of high gain, 1-10 MJ would be required. The physics, which must be investigated in this phase,

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is alpha particle bum propagation. People in United States say Centurion/Halite provides experimental evidence showing the feasibility of the high gain burning. For the commercial reactor development, we must investigate and develop high repetitive and high-efficiency drivers. In Japan, we are interested in only the civilian application of laser fusion. The driver for the high gain experiment and the driver for the reactor should have the same kind of technology for the continuation of the development. So we are thinking that the megajoule driver should have the technical continuation to the megawatt driver. In the demonstration of the commercial reactors, cost, environmental, and safety problems will be the key issues to be investigated.

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1 Instituteof Laser Engineering, OsakaUniversity. 227

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to a high gain experiment. The megajoule laser for this stage can be possibly constructed within 6--7 years. The most crucial technical problem toward a commercial reactor is the development and construction of high peak power pulse laser with high average output of megawatt. If we examine the technical feasibilities and estimate the length of the development and con-

struction, I believe, the prototype reactor construction could be in the 2020's. Nuclear fusion research must be strengthened because we need a new energy source for the next century. The recent progress of research and development have convinced us of the feasibility of inertial confinement fusion.

Journal of Fusion Energy, VoL 10, No. 3, 1991

Remarks of William Hogan I

drive energy. The figure also contains straight lines indicating the gain required to achieve certain yMds for a given drive energy. Recall that the LMF requirement is to achieve yields between 100-1000 MJ for conducting weapons physics and effects experiments. Note that the LMF baseline curves show a large uncertainty in the location of the "ignition cliff'' at the low drive energy end of the curves. LLNL's proposal for the LMF was to build a 4.5-6.0 MJ driver so that it would be about a factor of two away from the uncertain "ignition cliff" and so that yields of a few hundred megajoules could be achieved. There was also the possibility that yields up to 1000 MJ could be achieved at this drive energy if better coupling to the target than the LMF baseline proved achievable (upper curve). The NAS Interim Report recommended greater attention to certain Nova target physics experiments that would increase confidence in the ability to create drive conditions required for ignition. Reflecting on their recommendations, we asked ourselves if there was a target design approach that would allow study of target ignition at lower drive energy while maintaining hydrodynamic equivalence with the high gain targets ultimately desirable for the LMF. The answer we found is to operate at higher drive temperatures inside the hohlraum. Figure 2 shows three different gain curves. The one on the right uses the LMF baseline hohlraum temperature but assumes more conservative coupling assumptions than the LMF baseline curve of Fig. 1. Using the same coupling assumptions but re-designing the beam intensity and target design to achieve higher hohlraum temperatures, we calculated the other two gain curves shown in Fig. 2. These correspond to hohlraum temperatures 1.3 and 1.6 times that of the LMF baseline design. Note that the ignition cliff has moved significantly to the left. Now, the first question to be asked is: "what price have we paid?--what have we given up?" The drive energy is used in the target to do two things: some is used to create the correct ignition conditions in a small portion of the fuel, (i.e., high temperature and a suffi-

The Lawrence Livermore National Laboratory is very pleased with the National Academy of Sciences' (NAS) and the Fusion Policy Advisory Committee's final reports. Both have validated much of our work over the last 5 years since the last NAS review and are pointing toward a more vigorous future for the inertial fusion program. One of the issues that arose between the interim NAS Report and their final report was whether to focus near-term activities on a laboratory microfusion facility (LMF) whose goal would be to get large yield, and use it for weapon effects and weapon physics experiments, or on an upgrade of the Nova facility having the more modest goal of achieving ignition. I'd like to explain our decision to focus on the ignition upgrade for the near term while retaining the LMF as the long-term focus. Figure 1 shows our calculated gains for targets designed for our LMF proposal. These targets were designed to give the highest gain possible for any given

Fig. 1. Our LMF target design was based on driving the capsule close to the minimum radiation temperature and implosion velocity consistent with achieving ignition and gain, and, coincidentally, close to the maximum temperature and implosion velocity thought possible due to plasma physics limitations. 1 Lawrence Liverrnore National Laboratory.

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Fig. 2. Increasing implosion velocity for a fixed hydrostability criteria allows ignition and propagating burn at lower drive energy.

cient pr to force local deposition of alpha energy) and some is used to assemble the cold main fuel to a sufficient pr that it burns efficiently enough to give high gain. The LMF targets had been optimized to give the highest gain possible and thus the fraction of energy devoted to ignition was minimized. For the ignition targets, we devoted a greater fraction to creating the best ignition conditions and relaxed the requirement for high gain. As a result, the "ignition cliff" was moved to the left but the ultimate gain achievable at any given drive energy (once above the ignition cliff) is not as great. This trade also had to be done while preserving the in-flight aspect ratio and convergence limits imposed on the original designs so that they would be as conservative for stability as the original LMF targets. The final designs in fact, achieve the same pr as the LMF designs but less fuel mass is assembled. The next question we asked ourselves was" "what drive temperatures are achievable?" Our experience on Shiva had not been very promising for achieving higher temperatures than those of the LMF baseline, so we did some new ones on Nova with the shorter wavelength available. These recent Nova experiments indeed confirmed that we could achieve drive temperatures consistent with the center gain curve without running into plasma physics limits. Choosing to be as far to the right of the uncertain "ignition cliff" of the center gain curve as we were for our original LMF proposal, we then proposed that the drive energy for this ignition experiment should be about 1.5-2.0 MJ. Laser design studies then showed that such energies could be achieved by upgrading the Nova facility rather than by building an entirely separate, new facility. Thus was born the Nova Upgrade proposal to achieve ignition and gain by the end of the decade.

Hogan This proposal was endorsed by both the NAS and FPAC groups subject to confirmation of the target physics and laser design through a set of experiments described in detail in the so-called "LLNL Technical Contract." Assuming success for the Nova Upgrade project, Fig. 3 shows what the status of inertial fusion will be by the end of the decade in terms of the traditional Lawson diagram. All points shown as black dots have already been achieved. Nova has done both direct drive and indirect drive experiments in which different results were achieved. Improving the beam balance and pointing accuracy of Nova ("Precision Nova"), which is currently underway, should produce larger values of the quality of confinement. The Omega Upgrade and the Nova Upgrade are expected to achieve the parameters shown in the open circles. In particular, the Nova Upgrade should achieve ignition and gains of one to a few. Once ignition is achieved, we will explore target design variations to help us understand ignition scaling in greater depth. There will also be enough yield (x-ray, neutron, and debris fluxes) so we can begin to do some of the studies that will help us design the LMF and an engineering test facility (ETF) for the energy production application of ICF. We will be able to deal with the issues of first wall design and optics protection in a more realistic fashion. Thus, the Nova Upgrade will, by demonstrating ignition and gain, establish the laboratory feasibility of ICF. We can then make a more confident decision about the required size and design of an LMF for defense purposes and an ETF for energy purposes. We at LLNL are very optimistic about inertial fusion. We're gratified to see much of our previous work and current recommendations endorsed by both recent review committees in their final reports. Both reports

Fig. 3. ICF has made steady progress toward ignition and high gain.

Inertial Confinement Fusion

also encourage the ICF community to work closer together in the future. We fully endorse that recommendation. While it's true that competition is hea!thy and useful, it's also true that the next facilities are expensive enough, that they need to be usable by a large commu-

231

nity of people. We look forward to working with our colleagues in the other national laboratories and with other participants in the ICF Program toward the successes of the Nova Upgrade and the facilities beyond.

Journal of Fusion Energy, VoL 10, No. 3, 1991

Remarks of Guillermo Velarde 1

During this conference we have seen the latest theoretical and experimental results obtained in the field of nuclear fusion. According to the results and the recent published papers, we may conclude that:

several scientists in the field of ICF. This Manifesto calls for an aggressive program to design, build, and operate ICF facilities to demonstrate high-gain fusion in the laboratory. Achieving this goal will make possible the use of lCF technology for an environmentally attractive pure fusion source for electric power production, and advanced space propulsion. As a technology for a future fusion energy option, ICF has significant technological advances over the magnetic confinement approach and has become a highly credible alternative. Subsequently, several scientists joined the spontaneously founded International Society for Inertial Fusion Energy. At present, Prof. G. Velarde (DENIM) is the president, and Profs. N. G. Basov (Lebedev), C. Yamanaka (ILT), R. Dautray (Lirneil), and H. Hora (U. South Wales) are the vice presidents. A vice president from the U.S.A. has not been appointed yet. One of the aims of this society is to promote the creation of an international center of ICF similar to CERN. As it is said before, the U.S., U.S.S.R., and Japan are developing upgrading programs in their ICF facilities. Unfortunately, Euratom is following a risky route far from that of the above countries. About 97% of the Euratom fusion budget is devoted to magnetic fusion and only 3% to ICF. In order to solve this European problem, several initiatives have been taken:

1. The technology of inertial confinement fusion (ICF) has an advantage over magnetic confinement in that it is possible to separate the laser or accelerator driver from the reaction chambers, where the released energy is carried mainly by the neutrons in the D + T cycle. Thus, both the radioactive tritium and the neutrons that activate structural and cooling materials are confined in a much simpler reaction chamber, where inert materials, such as SiC, lithium, or ceramics can be used because of the much reduced vacuum and structural requirements. As a consequence, ICF power reactors can be inherently designed with very low material irradiation and radiological activation. 2. It has been shown (a) that the energy from a magnetic confinement tokamak reactor will be several times more expensive compared with light water uranium fission reactors, which are the most economical today. These very detailed estimates are still including optimistic assumptions and did not include the recent result that a commercial tokamak has a wall erosion of several millimeters per day of operation. (2) The lifetime of the first wall of a commercial ICF reactor is ten times the one of a tokamak.(3) 3. Underground test data summaries (3,4) indicate that ICF has at least as many scientific and technical possibilities as MCF.

1. The European Laser Facility: This initiative arose among Profs. Caruso (Italy), Fabre (France), Key (United Kingdom), Velarde (Spain), and Witkowski (West Germany) during the nineteenth ECLIM held in Madrid in 1988; however, Velarde was replaced by other Spanish delegates during its study. A report about its feasibility has been presented to the respective governments. 2. Nobel laureate N. G. Basov (Lebedev) has proposed, through the International Society for Inertial Fusion Energy and under the sponsorship of

Due to the remarkable progress in ICF during the last few years, several proposals for international collaboration have arisen. For instance, the Madrid Manifesto-inertial confinement fusion: The next step was signed by 1 Polytechnical University of Madrid.

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Velarde

UNESCO, the creation of an European Laser Center in a way similar to the role that Unesco played in the founding of the CERN in Geneva in 1954. 3. Prof. R. Dautray (Limeil) has proposed the use of the Laser PHEBUS of 20 kJ, the highest-energy laser in Europe, to be used for the EEC members in order to make experiments on laser interaction with the matter. The annual operating participation, personnel excluded, will be of 1.2 MECU. Prof. Dautray proposes also the construction of a new interaction chamber allowing spherical irradiation, with a participation cost of 15 MECU. 4. Nobel laureate C. Rubbia (CERN) has encouraged the groups working in heavy ion fusion in Europe to be coordinated under an elemental principle of common interest for presenting a program of work to be funded by the EEC and other countries. The first initiative has undergone several political im-

plications and it has lost interest at present due to the importance of the other three initiatives. Basov's is the most ambitious one and would place Europe at the same level as the U.S. or Japan. The initiative of Dautray is the most realistic and economical because it would allow an immediate start with certain experiments and to upgrade the PHEBUS afterwards. Maybe the best solution would be a mixture of the last three initiatives: to begin with Dautray's, while studies and projects are conducted to complete, during the next decade, a new CERN devoted to ICF, joining in this way Basov's and Rubbia's initiatives. REFERENCES 1. 2. 3. 4. 5.

D. Pfirsh and K. H. Schmitter (1989). Fusion TechnoL, 15, 1471. G. Vieider and G. Shatalov (Report ITER-TN-PC-8-9-1). M. Perlado and J. Sanz (1990). J. NucL Mater., 176. E. Storm et aL (U.S. Department of Energy). H. Hora et aL (1989). Pulsation free direct drive (Monterey Conference, Nov.).